Breeding improved tomato varieties involves providing genetics that give an advantage to the grower, processor, consumer, or other member of the supply chain. The improvement may be in the form of field performance, disease resistance, factory performance, or a fruit quality characteristic. For a tomato variety to be suitable to be grown for processing, the variety must have a concentrated fruit setting and maturity, firm fruit, and sufficient rot tolerance to allow early fruit to remain rot-free while later fruit continues to develop and ripen.
Most commercial processing tomato varieties are hybrids resulting from a cross pollination of two true-breeding, inbred parents. Through the use of true-breeding lines, a hybrid is produced that often displays characteristics of each parent, and often demonstrates characteristics that are superior to either parent alone, or that allow a hybrid to mask inadequacies of the individual parents.
Processing tomato varieties combining high levels of tolerance to bacterial canker (Clavibacter michiganense ssp. michiganense), early blight (Alternaria solani), late blight (Phytophthora infestans), and bacterial spot (Xanthomonas spp.) are highly desirable in humid climates where these diseases present production issues.
Moreover, combining resistance to tomato spotted wilt virus (TSWV) and race 3 of Fusarium oxysporum f.sp. lycopersici in tomato varieties adapted to arid climates is desirable to the processing industry in California and other global tomato processing regions where these diseases limit production. Further, Fusarium oxysporum f.sp. lycopersici race 3 (Fusarium 3) is a growing problem in the California tomato growing region and in other production areas worldwide, such as the Dominican Republic and Mexico. Productive, adapted varieties have been in demand by growers and processors since the mid 1990's with resistance to this pathogen. The disease has become a major limiting factor in tomato production in some California fields. Growers and processors need a range of tomato varieties with Fusarium 3 resistance, since product specifications vary with respect to juice viscosity, soluble solids content, field storage, and general field adaptability. Thus, varieties with resistance to either or both TSWV and Fusarium 3 are in high demand by both growers and processors to ensure a productive crop cycle.
An additional important contribution that tomatoes provide to the human diet is the antioxidant lycopene. Specifically, processing tomato varieties are the key form of tomato intake in the US diet. Higher levels of lycopene are beneficial both from a nutritional standpoint and from a consumer perception and quality standpoint. Tomato varieties having higher levels of lycopene result in products with a deeper red color that can be considered an indicator of higher product quality. Thus, a tomato variety with higher levels of lycopene, and improved color in general, can be valuable from both a nutritional standpoint and a quality standpoint. However, to be commercially viable and useful, the tomato variety must perform acceptably in the field and factory, as required by any other processing tomato variety. Previous varieties with increased lycopene levels have shown severe reductions in fruit quality, firmness, yield, and a sensitivity to fruit rots.